1. Field Of The Invention
The present invention relates to particulate material coated with a precured phenol-formaldehyde-furfuryl alcohol resin or a furan resin, wherein the precured resin coated particulate material is useful as a propping agent in fracturing, as particles in sand control, as a sand blasting abrasive or as a chemically resistant particulate material.
2. Description Of The Prior Art
Precured phenolic resin coated sands have been commercially available for use as propping agents. The term "precured" means that the phenolic resin coating is a cured coating, in contrast with particulate material coated with a curable phenolic resin, which is also commercially available.
The term "proppant" is indicative of particulate material which is injected into fractures in subterranean formations surrounding oil wells, gas wells, water wells, and other similar bore holes to provide support to hold (prop) these fractures open and allow gas or liquid to flow through the fracture to the bore hole.
The cured phenolic coating around individual particles of particulate material, such as grains of sand substantially increases the resistance of the sand grains to crushing under the high pressures encountered underground. However, there is a limit to the usefulness of these precured phenolic resin coated sands. This limit is dependent upon such factors as the increased pressure the proppant encounters at greater underground depths, and also the chemical resistance of the cured coating at the elevated temperatures and hostile chemical environment that exists underground. Thus, the cured coating can be exposed to temperatures in excess of 300.degree. F. and can contact various types of corrosive brine solutions at these temperatures. These very hot brine solutions can degrade the resin coating and thereby reduce the crush resistance of the resin coated sand.
In an effort to produce precured coated sand proppants having greater chemical resistance than that afforded by phenolic resins, various other types of precured resin coated proppants have been suggested using such resins as epoxy resins and furan resins. However, at this time, none have been accepted commercially and only precured phenolic coated sand proppants are now available for commercial use. A deficiency of these systems is the poor chemical resistance of precured phenolic coated sands at high pH. This is a concern in steam injection wells because the steam is highly alkaline and may strip the coating off.
The patent literature dealing with this technology includes U.S. Pat. No. 4,439,489 to Johnson et al which discloses a process for preparing particulate matter coated with a cured phenolic resin which comprises mixing an uncured resin with the particulate matter at a temperature of about 300.degree.-450.degree. F. in the presence of about 0.03-0.5% by weight of a lubricant, and maintaining the resultant mixture above about 300.degree. F. for a sufficient time to cure the resin, thereby obtaining a product containing individually coated particles having high abrasion resistance and improved crush resistance suitable for use as a propping agent in subterranean formations.
U.S. Pat. No. 3,935,339 to Cooke discloses coating particulate material with a liquid thermoset resin, preferably an epoxy resin, and agitating the coated particles with a liquid immiscible with the resin and containing a surfactant capable of retarding particle agglomeration as the resin cures to a solid state. A nonionic surfactant having a molecular weight of at least 2000 is preferred, and the resin is applied in sufficient amounts so that it constitutes from about 2-15 weight percent of the coated particle.
U.S. Pat. No. 3,492,147 to Young et al discloses a process for producing a resin coated particulate material in amounts wherein the particles are admixed or blended with a thermosetting resin or a polymerizable monomeric material in amounts sufficient to coat the individual particles, followed by curing the resin to a hard, infusible state, wherein the blending and curing is carried out under conditions such that little or no adherence between the individual particles occurs.
U.S. Pat. No. 4,443,347 to Underdown et al discloses a precured proppant charge comprising resin coated particles, each individually coated with a thermoset resin. The resin coating on the particles of the proppant produces a charge where the conductivity ratio throughout a given closure stress range is greater than that of a charge of the uncoated particles having substantially the same particle size distribution.